wtf: Set meta.mainProgram to "wtfutil"

This allows one to `nix run nixpkgs#wtf`.

pkgs/applications/misc/wtf/default.nix

@@ -38,6 +38,7 @@ buildGoModule rec {
     changelog = "https://github.com/wtfutil/wtf/raw/v${version}/CHANGELOG.md";
     license = licenses.mpl20;
     maintainers = with maintainers; [ kalbasit ];
+    mainProgram = "wtfutil";
     platforms = platforms.linux ++ platforms.darwin;
     broken = stdenv.isDarwin;
   };